There are some minute differences between PPO, HMO, and Indemnity.

One major difference is:

In PPO, you have the freedom to select any doctors, specialist, or hospital, anytime you wish from among the list of in-network providers of your insurance company. You can still go to out-of-network providers, but you might have to pay higher deductibles and higher co-insurance.

In HMO, you have to choose a primary care physician (PCP) who coordinates your care and refer to you specialists when necessary. In other words, you are restricted to only one doctor.

Depending on the deductibles, co-insurance, and the type of coverage you have, their premiums could be different, but everything else the same, you can see why HMO is little cheaper than PPO.

CDH is another very popular product. This is a bit tweak of PPO--the difference being CDH has  higher deductible and a health savings account. Because it has a higher deductible, it is bit cheaper than PPO by itself.

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If you are purchasing your insurance through your employer, I recommend you to stronly consider CDH, especially if you are healthy.